This invention relates to a circuit arrangement for selecting a diversity channel in a data transmission system.
Two or more diversity channels can be provided via which data are transmitted in accordance with a space diversity process, time diversity process or frequency diversity process. Each of the latter processes is well known and will not be described in detail herein. The data can be coded at the transmitting end using a convoluational code or using a block code, so that data faults are recognized on the basis of the received parity bits and information bits.
With known diversity processes the quality of the data transmission can be improved and the fault rate reduced. If, however, the receiving level is used as criterion for channel selection it is the channel which at a specific time is transmitting a signal with the relatively higher level which is switched through. This known process does not always lead to the desired success, and in particular when signals from an alien transmitter are transmitted with very high levels over a channel there is a risk these undersized signals will be received. This is particularly disadvantageous when the alien transmitter is an interfering transmitter so that the very channel which in no case should be switched through is in fact given perference.
A further difficulty in the selection of one of the diversity channels occurs when it is likely that all the existing diversity channels will be disturbed in such manner that frequently the correct code frame is not brought into phase at the receiving end.
An object of the invention is, therefore, to provide a circuit arrangement for selecting a diversity channel in which the channel selection is not made in accordance with the criterion of the receiving levels, and which operates satisfactorily even when the code frame is not yet known.